1. Field of the Invention
The present invention relates to a mobile terminal device that indicates the current position, and to a positional information system that includes this mobile terminal device and a base station for sending and receiving information.
2. Description of the Related Art
In recent years, the popularization of mobile terminal devices as represented by portable telephones has been remarkable, and this popularization has seen the development of mobile terminal devices having a variety of functions. The advent of mobile terminal devices that are capable of displaying the current position is just one example.
In a positional information system for acquiring positional information of the prior art, a GPS (Global Positioning System) receiver is provided in a mobile terminal device such as car navigation system, and radiowaves received from a plurality of GPS satellites are used to specify the current position of the device. The position is displayed on a map by superposing the current position of the device on map information that has been provided beforehand or on map information of the vicinity of the mobile terminal device that is transmitted from the base station that is set up in each of prescribed areas.
Known methods of specifying the current position of a mobile terminal device include a method in which the mobile terminal device is provided with a speed sensor and acceleration sensor and the output of these sensors is used to find the amount of movement from an initial position and thus specify the current position of the mobile terminal device, and a method in which the positional information that is calculated using the outputs of a speed sensor and acceleration sensor is used together with positional information that is obtained by the above-described GPS.
The positional information system of the above-described prior art can operate more effectively if a base station or the mobile terminal device itself can determine the state of the mobile terminal device, i.e., whether the mobile terminal device is currently stationary or in motion.
However, the mobile terminal device and positional information system of the prior art were not provided with a means for determining the state of the mobile terminal device at the base station or at the mobile terminal device itself.